The present invention relates to an increment sensor, transducer and/or pick-up and constructed for the conversion of either rotational or straight linear movements into a sequence of electric pulses, and more particularly the invention relates to a device of the foregoing kind which includes a light source or other radiation source and a photoelectric transducer and defining between them a monitoring or scanning gap in which a marking track moves, the track being established as a sequence of transparent or translucent markings alternating with opaque markings.
Increment transducers and pick ups of the type to which the invention pertains are generally known and are used, for example, for the open loop or closed loop control of machines, devices or other parts which usually undergo or are supposed to undergo a uniform movement, usually a rotational one or a reciprocal one. A particular example for example is the reciprocating motion of a carriage for a print head in a matrix printer. The matrix head drive runs uniformly and continuously or in uniform steps in order to move the part in between specific positions. Certain operations are to be carried out in these positions. In the case of a printer, of course, these positions are the print positions. The increment sensor generally and the photoelectric device in particular produces pulses which are fairly weak electrical pulses, and they are amplified in suitable circuitry to be raised to a more useful level for purposes of obtaining electrical control.
A known increment sensor is disclosed for example in German printed patent application No. 23 39 874. The particular construction of that publication is chosen to avoid a tumbling motion of the slotted disk vis-a-vis the scanning head. Moreover this known device is usually comprised of four photoelectric receivers such as photo transistors which are arranged along a line being oriented transversely to the direction of movement of the marking track. Each of the tracks will provide in the respective receiver a sinusoidal output and these outputs have respectively relative phase positions 0.degree., 90.degree., 180.degree. and 270.degree.. This multiple transducer arrangement is used in order to improve pick-up generally as far as the marking and slot distances are concerned. Accordingly two scanning devices for two sinusoidal signals are associated with a single slot. This arrangement is supposed to suppress the effect any tumbling motion of the disk in relation to the phase relations, pulse sequences is supposed to have. These phase relations are apparently easily adjustible because the two scanning devices, each including light source and receiver, are arranged on a common carrier which is pivotable and arrestable for pivot motion about a point which is situated between the two scanning devices. It was found, however, that an angle adjustment of the row of the transducers is not quite adequate to solve the problem; not even a major aspect of the problem because during initial installation and adjusting of the parts vis-a-vis each other further inaccuracies and tolerances arise, so that in fact the adjustibility of the increment sensors vis-a-vis two parallel arranged marking tracks becomes increasingly difficult.
Another aspect of the known device is that the mere mechanical adjustment of parts does not suffice. Particularly in the case of high speed operation electrical problems related to that high speed are encountered. Such a problem relates for example to the requisite adjusting of the operating point in the receiver and the transducers. Also, problems arise on account of varying operating temperatures of light source and receiver; the light source in particular is subject to aging if, as is common, such a source is constructed as a light emitting diode.
Another problem is to be seen in that any photo transistor when used as a pick-ip transducer offers per se two basic drawbacks. One drawback is that with rising temperature their gain increases while on the other hand with increasing frequency the gain reduces. The light emitting diode when used as source photo transistors because the luminous output decreases also with increasing temperature. However, this type of compensation is effective only if the temperature dependency of the photo transistor is at least approximately expressable by the same factor as the power drop of the light emitting diode. Generally speaking this equality cannot be expected. Therefor, on the basis of the physical conditions, manufacturing problems are to be expected.